Sandwich panels are often used in aircraft nacelle walls to dampen the effects of engine noise. A typical sandwich panel includes a honeycomb core with an inner face sheet and an outer face sheet. The inner face sheet is often perforated with a plurality of holes drilled or otherwise formed therein. Unfortunately, the drilling process will occasionally hit a cell wall of the honeycomb core beneath the inner face sheet, causing a structural defect. In the case of aluminum honeycomb cores, the drill may nick the aluminum, creating a corrosion point where a corrosion-protection primer on the core is inadvertently damaged and thus removed. Fiberglass honeycomb core may be less prone to this type of damage, but fiberglass core is typically more expensive than aluminum core and does not have the high thermal conductivity often desired for the inner duct wall of an aircraft nacelle.
It is possible to drill the perforations into the face sheet prior to attachment to the honeycomb core, but this can lead to some of the perforations being blocked by adhesive and cell walls, thus diminishing acoustic performance. Furthermore, this method requires additional cure cycles, and the additional thermal exposure limits the number of allowable repairs in the sandwich panel's life.
Accordingly, there is a need for improved methods and assemblies for fabricating nacelle sandwich panels without damaging the honeycomb core therein.